Update llvm/docs/SPIRVUsage.rst

Author: vmaksimo

llvm/docs/SPIRVUsage.rst

@@ -215,6 +215,8 @@ list of supported SPIR-V extensions, sorted alphabetically by their extension na
      - Adds a bitwise instruction on three operands and a look-up table index for specifying the bitwise operation to perform. 
    * - ``SPV_INTEL_subgroup_matrix_multiply_accumulate``
      - Adds an instruction to compute the matrix product of an M x K matrix with a K x N matrix and then add an M x N matrix. 
+   * - ``SPV_INTEL_int4``
+     - Adds support for 4-bit integer type, and allow this type to be used in cooperative matrices.
 
 To enable multiple extensions, list them separated by comma. For example, to enable support for atomic operations on floating-point numbers and arbitrary precision integers, use: